linux-kernel - Re: [PATCH 6/6] MIPS: net: BPF: Introduce BPF ASM helpers

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Date:	Thu, 13 Aug 2015 22:42:46 +0200
From:	Aurelien Jarno <aurelien@...el32.net>
To:	Markos Chandras <markos.chandras@...tec.com>
Cc:	linux-mips@...ux-mips.org, netdev@...r.kernel.org,
	"David S. Miller" <davem@...emloft.net>,
	Alexei Starovoitov <ast@...mgrid.com>,
	Daniel Borkmann <dborkman@...hat.com>,
	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	linux-kernel@...r.kernel.org, debian-kernel@...ts.debian.org
Subject: Re: [PATCH 6/6] MIPS: net: BPF: Introduce BPF ASM helpers

On 2015-06-04 11:56, Markos Chandras wrote:
> This commit introduces BPF ASM helpers for MIPS and MIPS64 kernels.
> The purpose of this patch is to twofold:
> 
> 1) We are now able to handle negative offsets instead of either
> falling back to the interpreter or to simply not do anything and
> bail out.
> 
> 2) Optimize reads from the packet header instead of calling the C
> helpers
> 
> Because of this patch, we are now able to get rid of quite a bit of
> code in the JIT generation process by using MIPS optimized assembly
> code. The new assembly code makes the test_bpf testsuite happy with
> all 60 test passing successfully compared to the previous
> implementation where 2 tests were failing.
> Doing some basic analysis in the results between the old
> implementation and the new one we can obtain the following
> summary running current mainline on an ER8 board (+/- 30us delta is
> ignored to prevent noise from kernel scheduling or IRQ latencies):
> 
> Summary: 22 tests are faster, 7 are slower and 47 saw no improvement
> 
> with the most notable improvement being the tcpdump tests. The 7 tests
> that seem to be a bit slower is because they all follow the slow path
> (bpf_internal_load_pointer_neg_helper) which is meant to be slow so
> that's not a problem.
> 
> Cc: netdev@...r.kernel.org
> Cc: "David S. Miller" <davem@...emloft.net>
> Cc: Alexei Starovoitov <ast@...mgrid.com>
> Cc: Daniel Borkmann <dborkman@...hat.com>
> Cc: Hannes Frederic Sowa <hannes@...essinduktion.org>
> Cc: linux-kernel@...r.kernel.org
> Signed-off-by: Markos Chandras <markos.chandras@...tec.com>
> ---
> I have uploaded the script and the bpf result files in my LMO webspace
> in case you want to have a look. I didn't paste them in here because they
> are nearly 200 lines. Simply download all 3 files and run './bpf_analysis.py'

This patch relies on R2 instructions, and thus the Linux kernel fails to
build when targetting non-R2 CPUs. See for example:

https://buildd.debian.org/status/fetch.php?pkg=linux&arch=mipsel&ver=4.2%7Erc6-1%7Eexp1&stamp=1439480000

-- 
Aurelien Jarno                          GPG: 4096R/1DDD8C9B
aurelien@...el32.net                 http://www.aurel32.net
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